I followed the installation instruction from the blueprint labs page and eclipse returned an error message stating that it was unable to find the download site. I then tried the url on the browser and it gave back the same error.

You cannot navigate to the download URL directly and install Blueprint from a broser. You have to use Flex Builder to install the plugin. When you provide Flex Builder with the download URL, it will look for a specific file (site.xml) that is hosted in that directory.